Conventionally, downsizing and capacity increase of magnetic disk apparatuses has progressed, and they are widely used in devices such as PDAs, portable phones, and car navigation devices, other than computers. Such a magnetic disk apparatus records information on a magnetic disk medium by using a head, and the non-contact type in which, as shown in FIG. 1A, a head 100 on which a head core 104 is disposed at a distal end of a head slider 102 flies over a medium surface by virtue of airflow 108 between it and the medium surface 106 is the mainstream. Meanwhile, in a low-temperature environment, for example in the winter, since the air density is comparatively high, the head 100 is caused to fly higher by the airflow 108 as shown in FIG. 1B, the head core 104 gets away from the medium surface 106, and the writing performance is reduced. When a write current is increased in order to compensate for such reduction in the writing performance, the large write current flows through the write core 104 and generates heat, the volume of the head core 104 is increased as shown in FIG. 1C due to thermal expansion, thereby causing projection of the head core 104, and the writing performance is increased since the head 100 is closer to the medium surface 106. Due to such a phenomenon of the head upon writing in a low-temperature environment, when data is written to sectors of a disk medium in a low-temperature environment, the writing performance is low at a top part of the sectors from which writing is started since the head core is not projected thereat, and the writing performance recovers during the writing since the head core is projected due to thermal expansion. Therefore, the phenomenon that the error rate is deteriorated at the top part of the sectors on which writing is performed and it becomes hard to be read occurs. In order to solve such problem of deterioration in the error rate in the low-temperature environment, under the current circumstances, screening of heads in which the heads which cause deterioration in the error rate at sector tops are eliminated is performed, and the head yield is therefore deteriorated. Also regarding completed magnetic disk apparatuses, screening of eliminating the apparatuses which cannot obtain a required error rate by a test operation in a low-temperature environment is performed, and the yield of the apparatuses is deteriorated. In order to solve such problem in manufacturing, in a conventional magnetic disk apparatus, write-verify read in which written data is immediately read and checked is executed, and write is performed again when it cannot be correctly read, thereby suppressing writing failure in a low-temperature environment (JP2003-141703). Moreover, as another method, a sector in front of a target write sector is once read and stored in a memory, pseudo-data is then written to respective sectors, and a process of writing data to the write sector from the sector in front together with the once read data is then performed, thereby ensuring stable operation in a low-temperature environment (JP2004-110918).    Patent Document 1: Japanese Patent Application
However, such conventional magnetic disk apparatuses have a problem that a write process in a low-temperature environment requires the processing time corresponding to that of several cycles of a disk, the processing time with respect to a write request from a host is increased, and the input/output performance is reduced. Moreover, the method of improving the error rate at the sector top part by increasing the write current has a problem that the write current for heating cannot be greatly increased since there is erasing influence to adjacent tracks since data areas are used, the restricted write current takes time in heating, and the error rate is deteriorated during that time. It is an object of the present invention to provide a highly reliable and responsive storage apparatus, storage medium, control method and program of the storage apparatus which can reliably perform write at the sector top part in a low-temperature environment without lengthening the processing time viewed from a host and without causing deterioration in the error rate.